Hotel barrier not opening from this time onwards (5)
I believe the answer is:
hence
'from this time onwards' is the definition.
(hence means from now on)
'hotel barrier not opening' is the wordplay.
'hotel' becomes 'h' (phonetic alphabet).
'barrier' becomes 'fence' (fence is a kind of barrier).
'not opening' means to remove the first letter (the opening letter is removed).
'fence' with its first letter taken off is 'ence'.
'h'+'ence'='HENCE'
(Other definitions for hence that I've seen before include "From this time, or for this reason" , "It follows from that fact" , "As a result" , "Therefore, consequently" , "In the future; begone!" .)